1. Field of Invention
The present invention relates to methods for dechlorinating organic compounds. More particularly, the invention relates to catalytic dechlorination of organic compounds comprising vicinal chlorides.
2. Description of Related Art
The compound 2-chloro-pentafluoropropene is useful as a soil fumigant (see, e.g., U.S. Pat. No. 2,785,984 (Kenaga)). Certain other soil fumigants, such as methyl bromide, are being phased out of commercial use due to their high ozone depletion potential.
Methods of preparing 2-chloro-pentafluoropropene are known. For example, U.S. Pat. No. 3,878,257 (Bruce) discloses the catalytic conversion of a propene, namely 1,1,2-trichlorotrifluoropropene-1, in the presence of HF and an anhydrous chromium (III) oxide catalyst with a divalent zinc ion to produce 2-chloro-pentafluoropropene. Although this method purportedly results in a conversion of 95-100 percent with a yield of 80 percent, it would be beneficial to produce 2-chloro-pentafluoropropene from more readily available starting materials, such as halogenated alkyls.
U.S. Pat. No. 2,917,558 (Cunningham, et al.) describes a method for producing 2-chloro-pentafluoropropene by zinc reduction of 1,2,2,3-tetrachloro-1,1,3,3-tetrafluoropentane to form a chloro-fluoropropene intermediate which is then treated with SbF3 to arrive at the intended product. Preparation of olefins via the dechlorination of organic compounds containing vicinal chlorines using elemental zinc is widely used today. However, this process is disadvantageous in that is generates a large amount of waste material as it utilizes an organic solvent and generates large quantities of zinc chloride as a by product. In addition, the process disclosed in Cunningham, et al. results in low yields of CF3CCl═CCl2 (i.e., only 27-29%). As a consequence, there has been some effort to find catalytic methods for the conversion of chlorofluoroalkyls to chlorofluoroalkenes.
Others have described reactions involving the catalytic dechlorination of chlorofluoroalkyls to produce hydrofluoroalkenes. For example, U.S. Pat. No. 2,697,124 (Mantell) discloses the catalytic dechlorination of certain chlorofluorocarbons, including 1,2-dichloro-1,1,3,3,3-pentafluoropropane and 1,1,2-trichloro-2,3,3,3-tetrafluoropropane, to produce an unsaturated product that retains substantially all fluorine atoms originally present in the reactant. Likewise, U.S. Pat. No. 5,714,655 (Yamamoto, et al.) discloses that 2,2,3-trichloro-1,1,1,3,3-pentafluoropropane and at least 4.5 equivalent parts of hydrogen in the presence of a noble metal catalyst and in the vapor phase will undergo a hydrogenation reaction to form 1,1,1,3,3-pentafluoropropane.
There remains, however, a need for an economical and environmentally friendly means of preparing 2-chloropentafluoropropene directly from a catalytic dechlorination of a chlorofluorocarbon. The present invention satisfies these needs among others.